There are several conventional methods for the cleanup and mitigation of fluid contaminants and more specifically indoor air contaminants, including, HEPA filters, electrostatic filters, biochemical filters, UV light, and ozonation. Photocatalytic oxidation (PCO) is a relatively new method that has been shown to be effective for disinfection of microorganisms and detoxification of volatile organic compounds (VOCs). The process involves the use of a photocatalyst in the presence of light of appropriate wavelength to oxidize organic compounds and microorganisms in fluids.
PCO involves the use of a photocatalyst such as Titanium Oxide (TiO2) for the destruction of hydrocarbons and microorganisms in fluids. TiO2 is a semiconductor photocatalyst with room-temperature band gap energy of about 3.2 eV. When this material is irradiated with photons having wavelengths less than about 385 nm (UV), the band gap energy is exceeded and electrons are generated through promotion from the valence band to the conduction band which results in the generation of electron holes (h+). The resulting highly-reactive electron-hole pairs have lifetimes in the space-charge region of the photocatalyst that enables participation in chemical reactions. The most widely postulated chemical reactions are:OH−+h+OH(hydroxyl radical)  (1)O2+e−→O2−  (2)
Hydroxyl radicals and super-oxides ions are highly reactive species that can readily oxidize volatile organic compounds (VOCs) adsorbed on catalyst surfaces. They can also kill and oxidize adsorbed bioaerosols. The process is a form of heterogeneous photocatalysts, or more specifically PCO.
Several attributes of PCO make it a strong candidate for indoor air quality systems. Pollutants, particularly VOCs, are preferentially adsorbed on photocatalytic surfaces and oxidized primarily to carbon dioxide (CO2). Thus, rather than simply changing the phase and concentrating the contaminant, the absolute toxicity of the treated air stream is reduced, allowing the photocatalytic reactor to operate as a self-cleaning filter.
Photocatalytic reactors may be integrated into new and existing heating, ventilation, and air conditioning (HVAC) systems due to their modular design, room temperature operation, and generally negligible pressure drop. PCO reactors also feature low power consumption, potentially long service life, and low maintenance requirements. These attributes contribute to the potential of PCO technology to be an effective process for removing and destroying low level pollutants in indoor air, including bacteria, viruses and fungi.
However, pollutant molecules or microbes need to come in contact with the catalytic surface as these electron-hole pairs are generated for any oxidation to occur. The probability of that happening in the fluid flow stream is very low. Current designs have a low efficiency in contaminant elimination since many contaminants in the fluid bypass or occur outside the reaction sites and survive on in the fluid. The source of the problem, as discovered by the inventor, is lack of contaminant contact with the catalyst reaction sites. This invention provides such an improved and useful method to bring these contaminants in contact with the catalyst reaction sites.